642 URINE. 



increased. It must not be overlooked that, as A. LOEWY l has found, 

 the sensitiveness of different individuals toward the action of acid 

 varies considerably. 



Although one cannot raise the degree of acidity of the urine above a 

 certain limit by the introduction of acid, still it may be easily diminished, 

 so that the reaction becomes neutral or alkaline. This occurs after the 

 taking of carbonates of the fixed alkalies or of such alkali salts of vege- 

 table acids citric acid, and malic acid as are easily burnt into car- 

 bonates in the organism. Under pathological conditions, as in the 

 absorption of alkaline transudates, or the alkaline fermentation within 

 the bladder, the urine "may become .alkaline. 



A urine with an alkaline reaction caused by fixed alkalies has a very 

 different diagnostic value from one whose alkaline reaction is caused by 

 the presence of ammonium carbonate. In the latter case we have to 

 deal with a decomposition of the urea of the urine by the action of micro- 

 organisms. 



If one wishes to determine whether the alkaline reaction of the urine 

 is due to ammonia or to fixed alkalies, a piece of red litmus paper, is dipped 

 into the urine and allowed to dry exposed to the air or to a gentle heat. 

 If the alkaline reaction is due to ammonia, the paper becomes red again; 

 but if it is caused by fixed alkalies, it remains blue. 



Determination of the Acidity. As the quantity of phosphoric acid 

 present as dihydrogen salt, as above stated, cannot be used as a measure 

 of the acidity, none of the older methods suggested for the estimation 

 of this portion of the phosphoric acid is suited for acidity determina- 

 tions. We now determine the acidity simply by acidimetric methods, 

 titrating with N/10 caustic alkali, using phenol phthalein as an indicator 

 (NAEGELI, HOBER, FOLIN) . On account of the color of the urine and the 

 presence of ammonium salts and alkaline earths, this method cannot 

 yield entirely exact results. The greatest error is due to the alkaline 

 earths, which, on titration with caustic alkali, precipitate as earthy 

 phosphates in variable amounts and of variable composition. This 

 error can be prevented, according to FOLIN, by the addition of neutral 

 potassium oxalate, which precipitates the lime, and in this way the 

 disturbing action of the ammonium salts is also inhibited. Perfectly 

 accurate results are not obtained by this method, but it is the best of 

 those which have been suggested. 



It is performed as follows: 25 cc. of urine are placed in an Er ] en- 

 meyer flask (about 200 cc. capacity), treated with 1-2 drops of -^-per cent 

 phenolphthalein solution, and shaken with 1520 grams of powdered 



1 Eppinger, Zeitschr. f. exp. Path. u. Therap., 3; with Tedesko, Bioch. Zeitschr., 

 16; Staal, Zeitschr. f. physiol. Chem., 58; A. Loewy, Centralbl. f. Physiol., 20, 337. 



